110 M. N. MEISSEL, E. M. BRUMBERG, T. M. KONDRATJEVA AND I. J. BARSKY 



fluorescence intensity and a characteristic shift in the fluorescence 

 spectrum. The change in colour of the fluorescence of the acridine 

 orange complex may be brought about either by the so-called concen- 

 tration effect, described as long ago as 1940 by Strugger or through 

 formation of dimeric and trimeric cations of the fluorochrome, a process 

 investigated by Zanker (1952). Both these effects in the cases under 

 consideration depend upon changes in the physico-chemical state of 

 DNA-protein or of DNA. Their binding with diaminoacridine increases 

 even in the initial stages of denaturation. It increases particularly on 

 depolymerization of the highly polymeric DNA, complexes being formed 

 of the type of those given by RNA with diaminoacridine. According to 

 the concepts being developed by Bradley and Felsenfeld (1959) the 

 degree of aggregation of acridine orange cations when the dye is being 

 bound with poly anions dejiends upon the configuration of the polymer. 



It is highly probable that the passage of DNA from the rigid bihelical 

 to the more mobile helical structure during denaturation is accompanied 

 by intensification of the dimerization of acridine orange cations. This 

 may serve as the explanation of the shift towards the right of the 

 fluorescence spectrum exhibited by the complex formed. Whichever 

 of the interpretations proves to be correct on further study one may 

 even now assert that the changes in intensity and colour of the fluores- 

 cence of nuclear structures in irradiated cells are manifestations of 

 important changes in the physico-chemical state of the nuclear nucleo- 

 proteins. These changes are evidently very widespread and may be 

 observed both in the cells of yeasts and in a variety of animal cells. We 

 have found them in the l)one-marrow of totally and locally irradiated 

 animals (Meissel and Sondak, 1955, 1956; Kondratjeva, 1956). They 

 appear immediately after irradiation, with doses from 100 r upwards, 

 in the form of individual cells or of cellular aggregates with sharply 

 changed and brilliantly fluorescent niiclei. Such aggregates formed as 

 the result of coalescence of the cells we have termed "micronecrotic." 

 The number of such micronecrotic foci increases with the dose and the 

 post-irradiation time (Figs. 1 and 2). The maximum number is found 

 6 hr after irradiation, following which they gradually disintegrate and 

 are resolved. The substance binding the cells into micronecrotic foci 

 energetically absorbs u.v. Hght with a wave-length of 280 to 254 jnju 

 and is apparently nucleic acid (Bukhman and Kondratjeva, 1959). In 

 bone-marrow cells of irradiated animals (900 r, 4 hr after irradiation) 

 there is a marked increase in absorption of u.v. rays of wave-length 365 

 m// (Kondratjeva and Bukhman, 1960). 



Similar cellular changes of focal character are found in the spleen 

 (Sondak, 1957) and in the lymph nodes and thymus of irradiated 



